1. Field of the Invention
The present invention relates to a nail printing apparatus, a controlling method of the nail printing apparatus and a computer readable storage medium with an executable program stored thereon, for precisely extracting a nail region of a nail of a finger or toe of a user where a nail design is to be printed.
2. Description of the Related Art
A nail printing apparatus has been proposed, which holds a finger of a user on its finger placing stand to print a nail design on the nail of the finger.
To define a printing region to print a nail design therein, it is necessary for the nail printing apparatus to detect the region of the nail (nail region) of the finger. A method of detecting the nail region of the finger is known, in which a camera is used to image the finger on which a nail design is to be drawn to acquire an image of the finger, and the nail region of the finger is detected from the acquired finger image.
For instance, Japanese Unexamined Patent Publication No. 2012-146182 discloses a so-called Watershed method used as the method of detecting a nail region of the finger. The “watershed method” is one of the methods of segmenting a region, in which a luminance gradient of an image is supposed to be a peak of a mountain and each place into which water flows from the peak of the mountain is segmented as one region. In the method disclosed in Japanese Unexamined Patent Publication No. 2012-146182, the place of the highest luminance is set as the starting point of a nail region and a region including the starting point is detected by using Watershed method, whereby the nail region is extracted from the image.
In general, when a finger of a human is imaged, the front portion growing from the nail floor side of the finger is higher in luminance than other portion and seems somewhat white. Therefore, even if Watershed method is used to detect the nail region of a finger, it is difficult to extract the front portion of the nail.